1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device. More particularly, the present invention relates to an in-plane switching (IPS) mode LCD capable of preventing signal interference of a data line and reducing vertical line deficiency.
2. Description of the Related Art
As various mobile electronic devices including a mobile phone, a PDA or a notebook computer are being developed, demands for light, thin, short and small flat panel display devices that can be applied to the mobile electronic devices are increasing. As a result, research for flat panel display devices such as an LCD (Liquid Crystal Display), PDP (Plasma Display Panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display) is actively ongoing. Of these displays, the LCD is most spotlighted because of its implementation in mass-production techniques, ease of a driving unit, and high picture quality.
A general LCD device implements an image by controlling light by using an electric field, including a liquid crystal panel on which pixels are arranged in a matrix form and a driving circuit for driving the liquid crystal panel.
FIG. 1 illustrates a unit pixel region of a related art IPS mode LCD. As shown, a gate line 1 and a data line 10 are arranged to cross each other to define a pixel region on a first substrate of the liquid crystal panel. A gate electrode 9, a semiconductor layer (not shown) and source and drain electrodes 13 and 15 are formed at the crossing of the gate line 1 and the data line 10, to form a switching device (e.g., a thin film transistor (TFT).
A pixel electrode 3 and a common electrode 5 are alternately arranged in each pixel region of the liquid crystal panel to generate an in-plane field on the first substrate. The pixel electrode 3 receives a data signal from the source and drain electrodes 13 and 15 of the switching device (TFT) and generates the in-plane field together with the common electrode 5 on the first substrate. In other words, the gate electrode 9 and the source and drain electrodes 13 and 15 are connected with the gate line 1 and the data line 3, respectively, to turn on the switching device (TFT) with a signal input through the gate line 1 and transfer a data signal applied through the data line 3 to the pixel electrode 3. As a result, the LCD displays an image by controlling the light transmittance of a liquid crystal layer with the electric field formed between the pixel electrode 3 and the common electrode 5 according to the data signal supplied to each pixel region.
Though not shown, a color filter layer is formed on a second substrate, and a liquid crystal layer is formed in a separated space between the first and second substrates.
In such an IPS mode LCD, since liquid crystal molecules of the liquid crystal layer are driven by the in-plane field formed between the pixel electrode 3 and the common electrode, a visibility range widens compared to the related art TN (Twisted Nematic) mode LCD, namely, obtaining a viewing angle of about 80°˜85° in all directions (up/down and left/right direction).
However, in the related art IPS mode LCD, because the data line 10 and the pixel electrode 3 are adjacent and parallel to each other, a signal interference is easily generated between the data line 10 and the pixel electrode 3, causing crosstalk and light leakage.
Thus, in an effort to solve such a problem, an outermost common electrode 5′ is disposed near the data line 10 and has a larger width compared to common electrode 5. However, such an electrode disposition structure degrades an aperture ratio of the LCD and distortion of the electric field due to the signal interference of the data line cannot be effectively prevented.
FIGS. 2A and 2B are enlarged views of the region ‘|’ in FIG. 1. The distortion of the liquid crystal array due to the signal interference according to a voltage variation of the data line will be described in detail with reference to FIGS. 2A and 2B.
A rubbing direction inducing an initial arrangement of liquid crystal molecules has about a 45° tilt to the common electrode 5 and 5′ and the pixel electrode 3, and an in-plane field generated when a voltage is applied to the common electrodes 5 and 5′ and the pixel electrode 3 is perpendicular to the common electrodes 5 and 5′ and the pixel electrode 3.
FIG. 2A shows that when a voltage of 8V is applied to the data line 10 and voltages of 5V and 8V are respectively applied to the common electrodes 5 and 5′ and the pixel electrode 3, a director of liquid crystal molecules is determined in a first direction 30 by an electric field generated due to a voltage difference between the common electrodes 5 and 5′ and the pixel electrode 3.
FIG. 2B shows that while a voltage of 8V is applied to the data line 10 and voltages of 5V and 8V are applied to the common electrodes 5 and 5′ and the pixel electrode 3, if the 8V applied to the data line 10 is changed to 10V, the direction of the electric field generated on the actual driving region of the liquid crystal molecules is changed to have the second direction 35 such that the director is rotated more than the first direction 30 shown in FIG. 2A.
The voltage change of the data line distorts the direction of the electric field in the pixel region, causing a change in the arrangement of liquid crystals. As a result, although the same voltage is applied to the common electrodes and the pixel electrode, the color sense is changed on a display screen.